Radial turbo compressors of the incipiently mentioned type are used in a wide variety of applications for compressing gas. The radial turbo compressor type is suitable for low pressure operation as well as for high pressure compression. The invention does not distinguish between a fan and a compressor regarding the pressure range. The compressor according to the invention is applicable in low pressure head operation as well. Specific advantages of the radial turbo compressor type are a high robustness and a high flexibility regarding volume flow and pressure difference.
Document FR 955 138 A discloses some aspects of the invention but does not consider exhaust gas recirculation. Some aspects of the invention are also shown in EP 2 924 261 A1.
Since radial turbo compressors normally are built bigger and heavier for the same volume flow capacity than axial flow compressors the axial machine type might be preferred for applications with limited space consumption requirements. Radial type machines tend to be more flexible and robust. Limited room availability not only restricts the final space requirement during operation of a machine but in most cases the assembly and maintenance is decisive regarding their feasibility with the available space.
It is therefore one object of the invention to provide an arrangement including a turbo compressor unit requiring less space during assembly and operation. This object is achieved by an incipiently mentioned type of an arrangement comprising the additional feature of the respective claim referring to such a component, wherein dependent claims refer to preferred embodiments of the invention.
The radial turbo compressor according to the invention comprises at least one impeller but can comprise several impellers as well. Preferably the impeller(s) is(are) mounted to a shaft. Preferably the shaft is supported by drive unit internal bearings exclusively. The drive unit is preferably provided as an electric motor.
Between the impeller and the inner components of the drive unit a shaft seal is preferably sealing the gap between the rotor shaft carrying the impeller and the stator of the motor and/or the stationary components of the casing of the turbo compressor.
An alternative preferred embodiment provides that the drive unit is connected in a gas tight or hermetically sealed manner to the turbo compressor casing. A drive unit casing is gas tight and the process gas delivered by the radial turbo compressor is floating into the drive unit casing.
In case, the process gas of the application intended is chemically aggressive the solution with the shaft sealing between the drive unit and the radial turbo compressor is preferred, for example in case the process gas is exhaust gas from a combustion engine.
According to the invention the turbo compressor is exclusively supported by the flange connections of the inlet flange and the outlet flange. This feature is to be understood that these flange connections are suitably build to transmit at least 95% of the mechanical load of supporting the turbo compressor against gravity as well as of supporting the turbo compressor against dynamic load from its own operation and from adjacent system excitation like pressure pulsations and vibration. The turbo compressor might be connected by other lines and pipes to allow supply of energy and maybe fluids for lubricating or cooling, but these connections don't transmit significant amounts of mechanical support load to keep the turbo compressor in its position. Since the support load is transmitted by means of the flanges to any adjacent structure like the inlet pipe of the turbo compressor the turbo compressor casing to which the flanges belong, is designed to transmit the mechanical forces of static and dynamic load to the connection flange of the adjacent module.
One preferred embodiment of the invention provides that the major part of the mechanical load to support the turbo compressor is transmitted via the inlet flange. Preferably the inlet flange is designed to carry at least 95%, preferably 100% of the dynamic and static mechanical load to the module the inlet flange is connected to by fixation elements.
A preferred embodiment of an arrangement comprising turbo compressor comprises an outlet pipe connected to the outlet flange of the turbo compressor comprising an elastic structure. This elastic structure preferably is designed to transmit low force via the outlet pipe. Alternatively the elastic structure can be embodied by the outlet pipe design and its support structure being made flexible such that mechanical load is not transmitted through this structure in a significant amount.
Another preferred embodiment of the invention provides that said casing comprises ribs in order to increase the bending stiffness of said casing, wherein said ribs distributed along the circumference of said casing extend radially at least partly between said drive unit flange and said inlet flange and extending in a radial direction along a rib's height. This rib structure enables the casing to transmit all mechanical dynamic and static loads originating from gravity and from dynamic excitation of the turbo compressor via the inlet flange of the casing into any adjacent module. These ribs provide sufficient stiffness to cope with supporting the mass of the drive unit being by said inlet flange, wherein the distance between the inlet flange and the center of gravity of the drive unit acts like a lever. The casing's preferred position in operation is a horizontal alignment of the axis (rotational axis), wherein the term ‘horizontal’ refers to the direction of gravity.
In order to further decrease space requirements of the turbo compressor according to the invention a preferred embodiment provides that said volute respectively a radial cross section area of said volute at each circumferential rib position is at least partly an integrated part of the respective rib at the specific circumferential position.
A further preferred refinement of this preferred embodiment provides that said casing of the turbo compressor comprises a circumferential outer first surface in an area which is not axially occupied by said outlet volute, wherein said outlet volute radially extends at least along 50% of the circumference with its radial cross section area in the same cylindrical plane as the radial outer first surface. This way the cross section area of the volute shares the same radial space with the cylindrical plane of the first radial outer surface. Since the radial cross section area of the volute is defined by an inner surface of a volute wall of specific thickness, the volute wall acts like a continuation of the ribs improving the stiffness against bending of the casing. Further this design safes radial space occupied by the turbo compressor enabling optimized aerodynamic design under restricted space availability.
Another preferred embodiment of the invention provides that said casing is casted in one piece comprising said inlet, said inlet flange, said outlet, said outlet flange, said outlet volute, said ribs, said radial outer first surface.
At least some of these ribs form together with the radial outer wall of said outlet volute a stiffening structure on the radial outer surface of the casing. Preferably this structure is in particular built to increase bending stiffness.
Another preferred embodiment provides that the casing comprises between 6 to 10 ribs, preferably 8 ribs, each extending axially and in the radial direction along a rib's height and at least some of these ribs comprise said outlet volute as an integral part with said outlet volute wall.
Another preferred embodiment provides that said casing is casted in stainless steel, wherein the preferred material is W 1.4408 (DIN: GX5 CrNiMo 19 11 2; ASTM: 316 A 743 CF-8M; this is a full austenitic Chromium-Nickel-Molibdaen-steal having good corrosion resistance). Casting the casing in stainless steel in one piece has the significant advantage that subsequent machining amounts to a minimum and is significantly less that if the casing would comprise several modules to be connected to each other.
The preferred embodiment of the casing provides the outlet volute to be semi external semi internal. As described and defined before the volute therefore has a radial cross section area. This cross section area is at least along 50%—preferably along 100% —of the circumference sectioned by a virtual cylindrical plane being defined by closely enwrapping—respectively tangenting—the radial outer surface of the casing omitting the ribs—respectively in the area which is not occupied by the ribs.
Another preferred embodiment provides an inlet chamber of the casing adjacent to the inlet flange being designed such that a sloped surface with regard to the axis respectively provides a safe drainage of any liquid collected in the inlet chamber into drain hold to avoid any liquid collection in the inlet chamber.
Another preferred embodiment of the invention is that the turbo compressor is part of an arrangement together with a pipe for a process gas or a recirculation line, wherein the recirculation line comprises a connection flange to which the inlet flange of the turbo compressor is fixedly connected to in order to transmit mechanical load from the turbo compressor to the recirculation line.
According to another preferred embodiment of the invention this arrangement further comprises a piston engine comprising an exhaust gas line for exhaust gas joining into said recirculation line conducting a portion of said exhaust gas into the turbo compressor. A further refinement of this arrangement according to the invention provides that the recirculation line is continued downstream the turbo compressor back into the piston engine for recirculation of a portion of the exhaust gas generated by said piston engine.
The preferred application of this invention is the recirculation of exhaust gas generated by a piston vessel engine to improve exhaust gas quality.
The invention further provides a method to retrofit a piston vessel engine by adding a turbo compressor according to the invention into a recirculation line or by adding a recirculation line comprising the turbo compressor according to the invention to a piston engine.
In FIGS. 1-7 same reference signs are used for same components. Expressions like circumferential, radial, tangential, axial refer to the axis X of the turbo compressor TCO if not indicated otherwise.